Radio frequency transformer



Dec. 19, 1922. 1,439,563. P. 0. LOWELL.

RADIOFREQUENCY TRANSFORMER.

ORIGINAL HLED SEPT. 9, 1921. 2 SHEETS-SHEET 1.

fereivdfl, ZIUwa-ZL azMW 47.

Dec. 19, 1922.

P. D. LOWELL.

RADIOFREQUENCY TRANSFORMER.

2 SHEETS-SHEET 2.

ORIGINAL FILED SEPT. 9, 1921- Cz'rcuii;

of 8 Sllcceediqg mcuum Tube gwuewfoz Ere iv aZD. Lowell Patented Dec. 19, 1922.

UNITED STATES PATENT OFFICE.

RADIO INSTRUMENT COMPANY, INC., BIA, A CORPORATION OF DELAWARE.

OF WASHINGTON, DISTRICT OF COLUM- RADIO FREQUENCY 'rnansronmnn':

Original application filed September 9, 1921, Serial No. 499,388. Divided and this application filed Jilly 1,

7 0 all whom it may concern:

Be it known that I,'PERCIVAL D. LOWELL, a citizen of the United States, residin at \Vashington, in the District of Colurn 1a, have invented a certain new and useful Improvement in a Radio Frequency Transformer, of which the following is a speclfication.

My invention relates broadly to the amplificatlon of radio frequency currents by thermionic vacuum tubes employed in the reception of radio telegraph and telephone signals and more particularly to radio frequency transformers associated with the circuits of the thermionic vacuum tubes.

This application is a division of my application Serial No. 499,388, filed Septemher 9, 1921-.

The principal object of the invention is to provide a construction of transformerpermitting the operation of radio frequency amplifiers efficiently at short wave lengths and which may be constructed for operation at any desired wave length over a wide band of wave lengths.

Another object of the invention is to pro vide a radio frequency transformer construe tion in which the capacity between the wind ings is a minimum.

A further objectis to provide a construction for variably coupling the primary and secondary windings of the radio frequency transformer, whereby the coupling may be set so as to, produce amplification at a particular wave length only or within a limited band of wave lengths, for selective reception.

A still further object is to provide a construction wherein a minimum capacity between the windings and the core is present.

Another object is to provide a transformer which is removable from the stages of the radio frequency amplifier to permit the ready substitution of a transformer having its windings designed and its coupling set for the particular wave length or band of wave lengths which it is desired to receive.

Radio frequency amplification of received signals through several stages is more desirable at.tl'ie radio receiver than initially rectifying the signal energy and then amplifying the alulio-frequeucy component alone. In radio frequency amplification the amplifier is quieter. that is, superfluous noises and in- Serial No. 572,112.

duction from dynamos are not amplified to as great a degree and a clearer signal is obtained than in the case of audio frequency amplification.

In general there are two methods of coupling between the stages of a multi-stage radio frequency amplifier, namely, transformer coupling and resistance coupling. Generally speaking transformer coupling is more desirable than resistance coupling because greater voltage amplification is pro duced per stage. It is true, however, that the transformer circuits must be tuned to the particular wave length, or in proximity thereto, at which the radio .frequency amplifier is to be operated, while the resistance coupled radio frequency amplifier although not producing as much radio frequency amplification per stage is advantageous because of its broader range of useful wave lengths.

Heretofore in the art it has been customary to construct radio frequency transformers for coupling the several stages of vacuum tube amplifiers, in two principal types; one of the shell type in which the primary and secondary windings are wound one beneath the otheron the central core of the shell frame; and the other in which thin fiat coils are employed and the primary and secondary arranged adjacent with their flat sides mutually parallel.

In the first construction there is inherently a high capacity between the two windings and a considerable capacity between turns as well as capacity to the core, all capacity effects restricting the wave. length range of the transformer, and also the amplifying effect, particularly at short wave lengths. In the second type there is also a considerable capacity between the primary and secondary and the transformer is inherently inefficient at short wave lengths by reason of the restricted coupling between the primary and secondary windings due to its air core and the small number of turns which may be employed on the windings at short wave lengths.

My invention will he more clearly understood by reference to the following specification and accom ninying drawings in which Figure 1 shows the connections of a multistage radio frequency amplifier together plification.

with a rectification stage and stages of audio frequency amplification with the present construction of radio frequency transformer interposed between the radio frequency stages of the thermionic vacuum tubes; Fig. 2 is a perspective view of the radio frequency transformer; Fig. 3 is a side view of the transformer showing the windings closely coupled; Fig. 4 is a side view of the transformer with the primary and secondary windings loosely coupled; Fig. 5 is a schematic diagram showing the electrical connections of the primary and secondary windings of the transformer; Fig. 6 is a perspective view showing the completed transformer removably mounted on the rear of the vacuum tube panel; Fig. 7 is a modified form of transformer construction.

Referring particularly to Fig. 1 of the drawings, a multi-stage thermionic. vacuum tube amplifier is shown comprising two stages of radio frequency amplifications, a rectification stage and two stages of audio frequency amplification. When used as a receiver of radio telegraph or telephone signals the inductance-1 is coupled to the radio frequency receiving circuit such as an antenna ground circuit, or a loop system may be employed as a collector of energy. The inductance is shunted by variable condenser 2 and connected in the input circuit of vacuum tube 3 forming the first stage of radio frequency amplification. The output circuit of vacuum tube 3 is connected to the primary winding 7 of the radio frequency transformer 6. The radio frequency transformer has its primary winding? adjacent secondary winding 8 and disposed on iron core 9. The secondary winding 8 connects to the input circuit of vacuum tube 4 form ing the second stage of radio frequency am- The output circuit of vacuum tube 4 is connected to the primary winding 11 of radio frequency transformer 10, having secondary winding 12 and the iron core 14. The secondary winding 12 of the second radio' frequency transformer connects through grid leak 17 and grid condenser 16 with the input circuit of vacuum tube 15 forming the rectification stage of the implifier. The output circuit of the vacum tube 15 contains the audio frequency transformer 18, which connects with the input circuit of vacuum tube 20 which is in turn connected through audio frequency transformer 21' potential for all of the tubes is supplied from battery B and the filament lighting current for the several tubes from battery A.

A variable resistance 5 is connected in circuitto vary the potential of the first and second grids of vacuum tubes 3 and 4- of the radio frequency amplifier.

secondary windings are disposed upon the supports 25 and 28 respectively, the primary winding 7 being wound in grooves 26 continuously from one end of the coil support to "the other, the winding in one groove being completed before the beginning of the Winding in the next adjacent groove 26. The secondary coil 8 is formed on support 28 by a winding in grooves 29, the winding'being completed in one groove and then progressing to the next adjacent groove. The preferred arrangement of the windings is that the coils progress from the grooves at the adjacent ends of the supports in opposite direc tions toward the ends of each of the supports.

The coil supports 25.and 28 may be variably coupled relative to each other. In Fig. 3 the windings are shown relatively tightly coupled while in Fig. 4 the primary and secondary windings are shown more loosely coupled to meet conditions in the reception of a particular frequency only, or over a limited range of frequencies. a

Fig. 5 is a schematic diagram of the primary and secondary windings of the transformer. The primary winding 7 which is connected to the radio frequency output circuit of one vacuum tube comprises a number of spaced coil sub-divisions, all of which may be relatively positioned with reference to the secondary winding 8 which connects to the input circuit of the succeeding vacuum tube. The secondary consists of a number of parallel spaced coil sub-divisions which by reason of their windings in the grooved coil support may be adjustably coupled relative to the primary winding.

. The radio frequency transformer is wound and its coupling fixed for a particular wave length or limited band of wave lengths which it is desired to receive. For different wave lengths over a broad band, the number of turns in the windings of the radio frequency transformer must be selectively chosen. In adapting the amplifier circuit of Fig. 1 for operation upon all wave lengths means are provided by which the radio frequency transformer for operation on the particular wave length band to be received may be readily inserted or removed. Fig. l?

' shows one form of mounting for the comthe entire rectangular case including the transformer and the contact terminals may be sprung into connecting clips 45, 46, 47

and 48. These connecting clips are secured to the rear of vacuum tube panel 41, which is vertically arranged and slotted at its top and bottom ends at 42, and 49 on the opposite sides of which spring clips 43 and H are arranged toform both supports for the vacuum tube 40 and also for a means for securing electrical connections forthe filament terminals and the grid and plate electrodes of the vacuum tube 40. Transformers for any wave lengths, constructed in accordance with this invention may be quickly inserted on the back of the panel and contacts made through clips 3345, 3446, 35-487 and 3548. Other forms of plug in mountings may be provided.

. Fig. 7 is a modification of the radio frequency transformer in which the primary and secondary windings are disposed on coil support 50 which encloses iron core 9. The primary winding comprises coils wound in grooves on the coil support and alternately connected as represented at 51. The secondary winding comprises coils 52 wound in grooves alternately positioned between the coils 51. The entire transformer may be readily mounted and enclosed in the casing represented in Fig. 6 by reference character 31. The transformer is cured within the case by frictional engagement with the inner walls of the case and by adherence with an insulating wax which forms a seal between the casing and the transformer.

By the particular construction of this transformer the total inherent capacity of the winding is small, for the reason that the several capacities are series connected. The capacity of the windings with respect to the core is much smaller than in other types of trans ormers in that there is a minimum area of the winding immediately adjacent the core.

While I have described my invention in certain preferred forms and specific embodiments I do not wish to be restricted to these forms, but merely intend to be limited within the scope of the following claims.

What I claim is:

1. In a radio frequency transformer, the combination of an iron core, a pair of thin walled coil supports enveloping said core and extending substantially respectively bepermanently se-;

tween each end and a central section of said core, and primary and secondarywindings carried by said supports and wound along their respective peripheries.

2. In a radio frequency transformer, the combination of an iron core, a pair of thin walled coil supports enveloping said core and extending substantially respectively between each end and a central section of said core, grooves spaced at intervals in the Walls of each of said supports, and primary and secondary coils wound in the grooves of the respective supports.

3. In a radio frequency transformer, the combination of an iron core, an inner casing enveloping said core, an outer casing enveloping said inner casing, a'pair of windings carried by said inner casing, terminals on the opposite exterior ends of said outer casing, and connections between said windings and said terminals.

4. In a radio frequency transformer, the combination of an iron core, a support enveloping said core and containing a plurality 0 I a n windings and said terminals.

5. Radio frequency transformer meanscomprising a plurality of transformer units, each having a primary and secondary winding, and detachable means for interchangeably and electrically connecting any one of said transformers separately from another to an external circuit, and means in each of said transformers for securing a different inherent coupling factor between said windings.

6. In a radio frequency transformer, the combination of an iron core, a. pair of thin walled coil supports enveloping said core and extending substantially respectively be tween each end and a central section of said core, grooves spaced at intervals in the walls of each of said supports, primary and secondary coils individually wound in the grooves of the respective supports beginning in grooves at adjacent ends of said supports and extending in opposite directions toward the end of each support.

7. Ina radio frequency transformer, the combination of a transformer unit, an insulated casing therefor, terminals carried by said casing and. arranged for detachable external connections with external circuits, said transformer unit including a primary and secondary winding connected with said initially locating said supports in position relative to each other whereby to fix the coupling factor of said windings, and sealing means within said casing preventing subsequent variation of said coupling.

8. In a radio frequency transformer, the combination of an iron core, a pair of tubular insulated supports frictionally engag ing said core whereby said supports may be longitudinally fixed in position relative to each other, a pair of windings carried by said supports, an external casing, and sealing means between said casing and said supports for permanently securing said supports in said fixed positions.

9. In a radio frequency transformer, the

combination of a rectangular laminated iron core, a pair of tubular coil supports mounted upon said core and spaced apart in fixed positions, grooves spaced apart in each of said coil supports, and subdivided primary and secondary coils wound in the grooves of the respective supports.

10. Radio frequency transformer means comprising a plurality of individual transformers, a supporting means for both interchangeably holding and electrically connecting said individual transformers to an external circuit, each of said transformers having a primary and secondar winding mounted to providediiferent coupling factors with respect to any other transformer.

11. Radio frequency transformer means comprising a. set of separate transformers, supporting means for both interchangeably holding and electrically connecting any one of said transformers, each of said transformers comprising a laminated iron core, a pair of tubular coil supports, grooves in each support, a multiturn primary and secondary winding disposed in the grooves of the respective supports, said supports said transformers one separately from the other, each of said transformers comprising an iron core, a pair of coil supports, grooves spaced apart in each support, a primary winding comprising a plurality of subdivided coils wound in the grooves of one of said supports, a secondar winding comprising a plurality of subdivided coils wound in the grooves of the other of said supports, said supports being mounted to fix the coupling between the respective windings of each transformer differently one from the other, a casing for each transformer, a set of contacts connected to said windings and carried on. said casing for quick contact with or removal from said resilient means whereby one transfolmcr may be quickly substituted for another of said transformers.

13. In a radio frequency transformer, the combination of an iron core, an envelope of insulation material surrounding said core. a primary and secondary winding disposed thereon, each winding comprising a group of coils, each coil having a plurality of fine wire turns wound along the periphery of said envelope and spaced from an adjacent coil, and the one group of coils spaced from the other group of coils whereby the coupling of said windings is permanently fixed fora particular band of frequencies.

PERCIVAL n. LoWELL. 

